A.turning right about, reversal of the normal order, Arist.HA590b13 ; esp. sudden change of condition or fortune, Id.Rh.1371b10 ; “π. τύχης” D.S.8.10 ; mostly from good to bad, Plb.1.13.11, etc.: less freq. from bad to good, Id.21.26.16, D.S. 4.43 : generally, any strange occurrence, unexpected event, Plb.9.12.6, 38.9.2, D.S.3.57, etc. ; ἐκ π. Arist.Po.1454b29, cf. Plb.32.8.4, Sch. BTIl.2.156.
2. esp. sudden reversal of circumstances on which the plot in a Tragedy hinges, such as Oedipus' discovery of his parentage, “ἔστι δὲ π. ἡ εἰς τὸ ἐναντίον τῶν πραττομένων μεταβολή” Arist.Po.1452a22, cf. 1450a34(pl.).
b. the plot itself, = ὑπόθεσις, S.E.M.3.3.